On a mining machine of the drum cutter type for extracting coal on the longwall principle there are three drives which are provided in current practice, especially where the mining machine is equipped to travel on top of, and be guided and supported by, a flexible armoured scraper conveyor which is laid along the working face.
These are:
1. The drive to the cutting means, i.e. the cutter drum. PA1 2. The drive to the means for hauling the machine along the longwall face, i.e. along the armoured face conveyor. PA1 3. The drive to the means for breaking up large lumps of coal which have been dropped or been guided on to the face conveyor during the cutting operation and which are required to pass below the mining machine body on their way to the ends of the coal face for subsequent transport to the surface.
As is well known, the positions of the cutting drum and the lump breaker are at the extremities of the machine.
The positions of the haulage drive output sprocket varies dependent on whether the haulage system is by a round link chain stretched along the face or whether the system is "chainless", i.e. rack and pinion, peg and sprocket or trapped round link chain sprocket. An example of the "chainless" system is shown in our U.K. Pat. No. 1,521,687.
If the haulage drive is via a round link chain stretched along the face, the machine haulage drive sprocket is usually positioned on the side of the machine approximately midway along its length. In the case of "chainless" drives, however, it is necessary to have the haulage drive sprocket mounted on or adjacent to the support shoes by which the machine rests on the armoured face conveyor so that undulations on the floor do not affect the pitch relationship which the sprocket has to its mating drive element secured to the armoured face conveyor. It so happens that it is also good practice to have the support shoes as close to the cutting element as possible because it is by these shoes that the machine is trapped to the armoured face conveyor and kept from rising due to the reaction force from the cutting means.
In many applications the seam height is fairly high and there is an optimum condition of choice between the cutting drum diameter, the ranging arm length and the height of under frame placed between the mining machine body and the armoured face conveyor to achieve the seam height to be cut. This condition allows the use of a lump breaker and a chainless haulage system, the latter being secured to the extremities of the under frame. However, for lower seams where the under frame height is such that it precludes the use of the latter as a means of locating and securing the "chainless" haulage drive unit, the unit is then secured to the end faces at the extremities of the mining machine and therefore precludes the use of a lumpbreaker mechanism which would normally occupy this position.